1. Field of the Invention
The present invention relates to a wireless communication system. And, more particularly, the present invention relates to feedback method for virtual MIMO (Multiple Input Multiple Output) transmission in wireless ad-hoc communication system.
2. Discussion of the Related Art
Distributed wireless network consist of multiple nodes distributed in a certain area where the nodes are able to organize clusters and to communicate with each other. Recently, since the rapid increase of nodes is required for high throughput and for the practical use of the MIMO system, a cooperative communication method, called as virtual-MIMO, has become one of the solutions.
FIG. 1 illustrates a concept of the virtual-MIMO transmission.
Referring to FIG. 1, in virtual-MIMO, uniformly distributed nodes with single antenna share their information and construct cluster to jointly transmit to the nodes cooperated to receive the data. However, there are still many challenging problems in this system. One of the main challenges is the channel state information (CSI) feedback in limited feedback (finite-rate feedback) environment. Two main objects of precoding are to mitigate the interferences and to customize the transmitted signal into the eigenstructure of the matrix channel with the knowledge of the channel. For precoding, the full CSI is required at the transmitter. In time-division duplex (TDD) systems, full channel state information is known that it is able to be adapted by the reverse-link signal-to-interference-and-noise ratios (SINRs).
However, in frequency-division duplex (FDD) systems, CSI is known at the transmitter through feedback channel. In practical system, the effects of the limited feedback are important issues to design a virtual-MIMO system in distributed wireless network. In prior art (e.g., Hierarchical Cooperation Achieves Optimal Capacity Scaling in Ad Hoc Networks, IEEE Trans. Inform. Theory, vol. 56, no. 3, pp. 1369-1377 2007.), the virtual-MIMO transmission with nodes cooperation shown optimal capacity scaling are studied, and a hierarchical cooperation system is introduce, where there is a main communicating clusters divided into sub-clusters hierarchically for data sharing. However, it does not consider limited feedback environment. The motivation of this patent is to propose an efficient CSI feedback system using virtual-MIMO transmission in distributed wireless network.